DISTRIBUTED FIBER OPTIC SENSOR SYSTEM WITH IMPROVED LINEARITY
First Claim
1. A method of detecting a change in a parameter of interest incident along the length of an optical fiber sensor deployed in a region of interest, comprising:
- providing a first optical signal output by a narrowband optical source in a first optical path and a second optical signal output by the narrowband optical source in a second optical path;
modulating the first optical signal to generate a plurality of probe pulses;
launching the probe pulses into an optical fiber sensor deployed in a region of interest, the optical fiber sensor configured to respond along its length to a parameter of interest;
mixing Rayleigh backscatter signals generated by the optical fiber sensor in response to probe pulses with the second optical signal to generate intermediate frequency (IF) signals;
determining phase of the IF signals at a plurality of locations along the optical fiber sensor; and
detecting a change in the parameter of interest along the length of the optical fiber sensor based on differences in the determined phases across a selected interval between the plurality of locations.
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Abstract
A fiber optic sensor system includes an optical source to output a first optical signal to launch into an optical fiber, and a coherent detector to mix a coherent Rayleigh backscatter signal generated by the optical fiber in response to the first optical signal with a second optical signal output by the optical source and to generate a mixed output signal. A phase detection and acquisition system determines a phase difference between first and second locations along the optical fiber based on phase information extracted from the mixed output signal and combines the phase information extracted from multiple acquisitions to detect strain on the optical fiber sensor.
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Citations
28 Claims
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1. A method of detecting a change in a parameter of interest incident along the length of an optical fiber sensor deployed in a region of interest, comprising:
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providing a first optical signal output by a narrowband optical source in a first optical path and a second optical signal output by the narrowband optical source in a second optical path; modulating the first optical signal to generate a plurality of probe pulses; launching the probe pulses into an optical fiber sensor deployed in a region of interest, the optical fiber sensor configured to respond along its length to a parameter of interest; mixing Rayleigh backscatter signals generated by the optical fiber sensor in response to probe pulses with the second optical signal to generate intermediate frequency (IF) signals; determining phase of the IF signals at a plurality of locations along the optical fiber sensor; and detecting a change in the parameter of interest along the length of the optical fiber sensor based on differences in the determined phases across a selected interval between the plurality of locations. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. An apparatus, comprising:
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a narrowband optical source to output a first portion of an optical signal to a first optical path and a second portion of the optical signal to a second optical path; a modulator to generate a first probe pulse and a second probe pulse from the first portion of the optical signal to launch into a fiber optic cable deployed in a wellbore formed in a region of interest, the fiber optic cable configured to respond to a parameter of interest incident along its length; an optical detector to mix a Rayleigh backscatter signal generated by the fiber optic cable in response to each of the first and second probe pulses with the second portion of the optical signal to form a first intermediate frequency (IF) signal corresponding to the first probe pulse and a second IF signal corresponding to the second probe pulse; and a phase detection and acquisition system to determine a phase difference for each of the first and second IF signals between a plurality of locations along the fiber optic cable, and to compare the phase differences as a function of the locations, wherein the compared phase differences are indicative of changes in the parameter of interest incident on the fiber optic cable. - View Dependent Claims (17, 18, 19, 20, 21)
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22. A system to detect a parameter of interest, comprising:
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an optical fiber sensor to deploy in a wellbore formed in a region of interest, the optical fiber sensor configured to respond to strain incident along its length; an optical source to output a first optical signal to provide to the optical fiber sensor; a coherent detector to mix a Rayleigh backscatter signal generated by the optical fiber in response to the first optical signal with a second optical signal output by the optical source and to generate an output signal from the mixed signals; and an acquisition system to determine phase differences between locations along the length of the optical fiber sensor based on phase information extracted from the output signal, wherein the phase differences are indicative of strain incident along the length of the optical fiber sensor. - View Dependent Claims (23, 24, 25, 26)
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27. A method of detecting a parameter of interest incident along the length of a distributed fiber optic sensor, comprising:
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launching a plurality of probe pulses generated by an optical source into a distributed fiber optic sensor configured to respond along its length to a parameter of interest that is incident thereon; mixing Rayleigh backscatter signals generated by the distributed fiber optic sensor in response to the probe pulses with an optical signal generated by the optical source to generate mixed output signals, wherein each mixed output signal corresponds to a particular one of the probe pulses; for each mixed output signal, determining phase differentials between locations along the distributed fiber optic sensor; and comparing the phase differentials determined for a first mixed output signal with the phase differentials determined for a second mixed output signal as a function of location to detect a change in the parameter of interest along the length of the fiber optic sensor.
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28. An optical time domain reflectometry system, comprising:
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a distributed fiber optic sensor deployed in a region of interest, the distributed fiber optic sensor configured to respond along its length to a parameter of interest; a coherent optical source to output a first portion of an optical signal to a first optical path and a second portion of the optical signal to a second optical path; a modulator in the first optical path to generate a plurality of probe pulses from the first portion of the optical signal to launch into the distributed fiber optic sensor; a coherent detection system to mix Rayleigh backscatter signals generated by the distributed fiber optic sensor in response to the probe pulses with the second portion of the optical signal to generate mixed output signals, each mixed output signal corresponding to a particular one of the probe pulses; and a phase detection and acquisition system to determine, for each mixed output signal, a phase differential between first and second locations along the length of the distributed fiber optic sensor, and to compare the determined phase differentials to determine a change in the parameter of interest between the first and second locations.
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Specification